docs: def _removecleaner(self, cleaner):
          """
          Remove the cleaner from the list if it already exists. Returns True if
          the cleaner was removed.
          """
          oldlen = len(self._old_cleaners)
          self._old_cleaners = [
              oldc for oldc in self._old_cleaners
              if not oldc.issame(cleaner)
          ]
          return len(self._old_cleaners) != oldlen